EPA Section 608 Universal Certification ExamType II (High-Pressure Appliances)Hard
A technician is performing a major repair on a high-pressure appliance and has recovered the refrigerant. The next step is to evacuate the system. To prevent liquid refrigerant from flashing into vapor and potentially freezing water in the vacuum pump, what is the best practice before starting the evacuation?
- ARapidly open the vacuum pump valve to draw a deep vacuum quickly.
- BHeat the system components to a temperature above ambient.
- CPurge the system with a small amount of liquid refrigerant.
- DIntroduce a small amount of nitrogen into the system.
Show answer & explanationAnswer & explanation
Correct answer: D. Introduce a small amount of nitrogen into the system.
Introducing a small amount of nitrogen (or dry air) into the system will raise the system pressure above atmospheric, preventing any residual liquid refrigerant from flashing to vapor and potentially freezing water in the vacuum pump as the vacuum is pulled. This also helps to 'push' any remaining refrigerant out.
Why the other options are wrong
- A. Rapidly opening the vacuum pump valve can cause a sudden pressure drop, increasing the likelihood of residual liquid refrigerant flashing and freezing moisture.
- B. Heating system components can help boil off moisture, but it doesn't directly prevent liquid refrigerant from flashing if the system is still under vacuum or low pressure.
- C. Purging with liquid refrigerant would add more refrigerant, defeating the purpose of recovery and evacuation.
Preventing Vacuum Pump Contamination
Techniques used to protect the vacuum pump during evacuation from damage caused by liquid refrigerant or excessive moisture.
- Nitrogen sweep prevents flash-off.
- Use a vacuum pump with a gas ballast.
- Change pump oil regularly.
Memory trick: To protect the pump, 'Nitrogen' is the dry shield!